1. Preheat your oven to 350 F (175 C). Grease and flour a 9×5-inch loaf pan, or spray generously with non-stick baking spray.

2. In a large mixing bowl, using an electric mixer, cream together the softened butter and granulated sugar until the mixture is light, fluffy, and pale in color. This usually takes about 3-5 minutes.

3. Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Scrape down the sides of the bowl as needed. Stir in the vanilla extract until just combined.

4. Gently fold in the sourdough discard until it is evenly mixed into the wet ingredients.

5. In a separate medium bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking soda, and salt. Make sure there are no lumps of cocoa powder.

6. Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix on low speed until just combined after each addition. Be careful not to overmix. If using, fold in the chocolate chips at this stage.

7. Pour the batter into your prepared loaf pan and spread evenly. Bake for 50-60 minutes, or until a wooden skewer or toothpick inserted into the center of the cake comes out clean. The top should be nicely domed and firm to the touch.

8. Once baked, remove the cake from the oven and let it cool in the pan for about 10-15 minutes before inverting it onto a wire rack to cool completely.